From Longman Dictionary of Contemporary Englishmilli-milli- /mɪlə, mɪlɪ/ prefix [in nouns] TMa 1,000th part of a unit a millilitre (=0.001 litres)
Examples from the Corpus
milli-• a milliliterFrom Longman Business Dictionarymilli-milli- /mɪlə/ prefix a 1,000th part of a particular unita millimetreOrigin milli- French Latin, from mille “thousand” 